Field of the Invention
The present invention relates generally to environmental control of buildings suited for human occupancy. More particularly, the present invention relates to the control of such environmental parameters as temperature, humidity, particulate levels, or even specified gas levels such as carbon dioxide (CO2) at increased efficiency.
State of the Art
Indoor air quality and environmental control is of great concern with regard to both residential and commercial buildings. Occupants of such buildings desire to utilize these buildings in comfort and in safety. In typical heating, ventilation and air conditioning (HVAC) systems, many environmental parameters, such as temperature, humidity, and other air quality parameters, may be controlled. Typically, control of these and other environmental parameters entails, among other things, movement of air within the building, which can include introduction of fresh air from outside the building or circulation of existing air within the building. In controlling a building""s environment, air may be passed through furnaces, across refrigerated coils, or through humidification devices prior to introduction of the air into the occupied regions of the building. Control of an HVAC system may also include the combination of more than one of the above techniques to control multiple parameters within the building""s environment simultaneously.
A typical method of controlling the air movement and other environmental parameters within a building is through the cyclical control of fans, or blowers, which are an integral part of an HVAC component known as an air handling unit. For example, when it is desired to cool the building, or a particular space within the building, the air handling units are turned on when the temperature rises above a predetermined upper level and then shut off when the temperature of the facility reaches a predetermined lower level. A system of this type is generally described in U.S. Pat. No. 4,682,473 to Rogers, III. This type of system utilizes the fans at full power, allowing them to cool or heat the facility at a relatively quick pace within a specified temperature range. Such systems, however, possess a number of shortcomings. For example, rapid changes in temperature, or temperature spikes, may often result in some discomfort for the occupants. Similarly, rapid changes in other environmental parameters may cause occupant discomfort. Furthermore, cyclical use of air handling units at full power or full speed may result in inefficient control of such parameters.
Other known systems have sought to utilize multi-speed or variable-speed fans in controlling an HVAC system. Such a system is described in U.S. Pat. No. 5,492,273 to Shah, which includes a variable-speed blower motor for controlling the volumetric rate of airflow within the system. This type of system allows for a more gradual and natural change of an environmental parameter within defined parameter ranges. However, because the system is still cyclical in nature, it does not provide control of the building environment at a desirable level of efficiency. For example, in controlling temperature, the fans will remain inoperative if the temperature of the facility is within a defined temperature range. The fans will then operate at a predefined speed setting once the temperature increases into a second defined range. The blower continues to operate for a time period calculated as the expected interval of operation. If at the end of the expected interval of operation the temperature is not within the desired range, the blower will increase its speed to more quickly effect the desired temperature change. Once the desired temperature has been reached, operation of the blower is terminated until the temperature falls outside of the prescribed range once again. The fans will operate at a high-speed setting if the temperature increases into a third defined range.
All of the above techniques, due to their cyclical nature, include defining a range of operation, such as a temperature range. However, it is difficult to narrowly define the ranges. If the ranges are defined too narrowly, the air handling unit will repeatedly start and stop as the parameter fluctuates in and out of the prescribed range. Such incessant starting and stopping is likely to cause wear and fatigue-type damage to various components of the air handling unit, such as starters, motors and mechanical transmission components. On the other hand, if the defined ranges are set too broadly, high temperatures may cause the fans to operate at the high-speed setting for extended periods of time in an attempt to bring the temperature back to an acceptable value. Such overuse of air handling units at full speed or power results in an inefficient HVAC system. Furthermore, a broad parameter range may simply not be acceptable from a comfort standpoint.
As noted above, an important consideration in the environmental control of a commercial or residential building is the efficient use of power. With air handling units which are cyclically controlled, power consumption is of paramount concern to those responsible for the maintenance of the building. Occupancy of such buildings for any extended period of time requires a significant consumption of power with existing systems and methods. The cost of such power is ultimately borne by the occupant. Thus, an efficient and accurate environmental control system for such buildings would be of benefit to both the owners and tenants of the buildings.
In view of the shortcomings in the art, it would be advantageous to provide an environmental control system for commercial and residential buildings which effectively controls specified environmental parameters while consuming a reduced amount of energy. Such a system or method should be simple to employ in existing as well as newly constructed buildings.
In accordance with one aspect of the invention, a method is provided for controlling the internal environment of a building intended for human occupancy, such as a commercial or residential building. The method includes the steps of providing a fan, or a plurality of fans, for circulating the internal air of the building. The fans may be operated continuously at a speed which is below their full capacity to achieve continuous parameter control at reduced power consumption. The system monitors a parameter indicative of the internal environment of the building, such as the internal temperature. Once the temperature has been monitored, the speed of the fans is altered accordingly. If the internal temperature needs to be reduced, then the fans may be operated at a higher incremental rotational speed to increase the air movement within the building. Likewise, if the air temperature needs to be increased, the fan speeds may again be incrementally altered. The same method may be employed to effect changes in airflow rate in order to obtain a desired value for various target parameters.
Additionally, environmental parameters outside of the building may be monitored to assist in the regulation of airflow in the internal environment. For example, external air temperature may be monitored, compared to the desired building temperature, if desired, and admitted into the building via a ventilation inlet. Various restrictions may be placed on the admittance of outside air, such as preventing outside air from being introduced into the building when the outside temperature is above or below a predetermined target or range.
The method may also include conditioning the air which is provided to the internal environment. Such conditioning may include, for example, passing the air over heating or cooling coils, subjecting the air to a filtering process, or subjecting the air to a process of humidification or dehumidification.
In accordance with another aspect of the present invention, a system is provided for controlling the internal environment of a building designated for human occupancy. The system includes an air handling unit, including a fan or multiple fans that are adapted to operate continuously. The fans are configured to allow their continuous operation at speeds which are below their operational capacity. More specifically, each fan is coupled to a variable-speed drive for controlling the operational speed thereof. At least one sensor is employed to monitor one or more internal environmental parameters of the building, such as temperature, humidity, gas levels, or particulate levels. The sensor is coupled to an electronic control unit which is, in turn, coupled to at least one of the variable-speed drives. The sensor provides a signal to the electronic control unit, the signal representing a measured value of an internal environmental parameter. The electronic control unit then provides a signal to the variable-speed drive based upon the sensed parameter, causing the associated fan to vary in speed accordingly.
Additional elements may be configured with the system to render greater control and flexibility. For example, sensors monitoring an external environment may be coupled to the electronic control unit to assist in determining fan speed. Ventilation inlets or outlets may also be coupled to the electronic control unit for controlling flow of air into and out of the building, respectively.